Method of producing transformation hardenable stainless steel and articles produced therefrom



% CHROM/UM July 14, 1959 R. SMITH 2,894,867

METHOD OF PRODUCING TRANSFORMATION HABDENABLE STAINLESS STEEL AND ARTICLES PRODUCED THEREFROM Filed July 11, 1957 AN/VEALl/VG' TEMR CHROM/UM 30 x 04,950 NICKEL Ella-. E-

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30X CARBON NICKEL INVENTOR RAYMOND sM/m A Home? METHOD OF PRODUCING TRANSFORMATION HARDENABLE STAINLESS STEEL AND ARTI- CLES PRODUCED THEREFROM Raymond Smith, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey -Applicafion July 11,1957, Serial No. 671,213 12 Claims. (Cl. 148-2155) This invention relates to production of transformation hardenable stainless steel and more particularly to aus- .tenitic stainless steel which is hardenable by low temperature transformation.

' In the construction of modern aircraft, guided missiles and the like, there is needfor steels having good high temperature and, corrosion resistance properties which can be fabricated in the soft austenitic condition and later transformed to the desired minimum hardness of RockwelljC39 or a tensile'strength of 180,000 p.'s.i. Steels which harden by precipitationare unsuitable for prolonged use at temperatures approaching or above the hardening'temperature due-to their tendency to soften. I have found that these desired properties can be'pro- "duced 'by the proper heat treatment of a steel containing about 15 to 18% chromium, about .55 to 1.75% vanadium together with carbon and nickel within certain critical limits as more fully described hereinafter. Such steelhas the following general composition limits:

Percent Carbon .03 to .30 Manganese 5.. .50 to 2.0 "Silic'on a .20 to 1.50 Nickl- 3.0 to 7.5 Chromium 15.0 to 18.0 IVan adium .55 to 1.75

:balance substantially iron and other elements in amounts whichdo not adverselyaftect the properties.

' .Within such limits theferrlt formers and austenite formers must be balanced to provide an M, point in the steel which is below room temperature and preferably between about F. and 50 F. The vanadium content 2,894,867 Patented July 14, 1959 lrange of 700 to 1100 F. and preferably at about 800 F.

to produce a tempered martensitic structure therein.

Figures 1 and 2 of the accompanying drawing which are graphs wherein the ordinates denote the percentage of chromium and the abscissas the sum of the product of 30 times the percentage of carboncontent plus the percentage of nickel. The shaded areas ABCD. and A B C D represent the amounts of chromium and com bined amounts of carbon and nickel which will give the desired results with the particular austenitizing treatment shown. Thus Figure l depicts the best composition for an 1800 F. austenitizing temperature and Figure 2 the composition requiring a 2000 F. austenitizing temperature. Steels having compositions falling to the right of the lines AB, and A 3 do not transform or harden to a satisfactory degree whereas those falling to the left of the lines CD, and C D transform and harden upon cooling to room temperature after annealing.

The following Table I lists the composition of a numher of heats which are illustrative of the steels of my invention: Table 1 Heat 0 M11 P 8 s1 N1 Or V 801.

The eifect of various annealing temperatures on these is shown in the following Table II.

, Table -II V 15 Min. 1,800 F., W.Q.' 15 Min. 1,900 F., W.Q. 15 M1n.2,000 F., W.Q. 15 Min. 2,050 F., W.Q.

Rockwell Hardness Rockwell Hardness Rockwell Hardness Rockwell Hardness 7 Heat Annealed 2 Hr. 1l0 F. Annealed 2 Hr. -1l0 F. Annealed 2 Hr. 1l0 F. Annealed 2 Hr. F. +2 Hr. 800 F. +2 Hr. 800 F. +2 Hr. 800 F. +2 Hr. 800 F.

033. 5 C40. 0 B96. 0 G43. 5 B98. 5 C 39. 6 B94. 0 C45. 0 C38. 5 C44. 0 B96. O 045. 0 B95. 0 044. 0 B95. 0 C43. 0 043. 5 C43. 0 B97. 0 C46. 5 B92. 5 C42. 5 B94. 0 045. 0 C31. 0 G47. 0 B99. 0 C47. 0 B91. 5 C45. 0 B91. 5 047. 0 044. 0 C47. 5 034. 0 046. 0 021. 5 C46. 0 B95. 5 042. 0 038. 5 047. 5 C36. 0 047. 0 B98. 5 C40. 5 B98. 5 036. 5

The following Table 111 lists certain steels which were martensit'ic'as annealed.

Table III Heat Mn P 8 s1 N1 Or V 501.

Typical steels which were austenitic as annealed and *Showed -15% delta ferrite in annealed condition.

A preferred embodiment of the steel of my invention for developing hardness value in excess of C'45 or tensile strengths in excess of 220,000 p.s.i. contains Percent Carbon .15 to .26

Manganese .75 to 1.20 Silicon .35 to .75 Nickel 3.40 to 5.6 Chromium 16.0 to 17.3 Vanadium .60 to 1.20

Steels of this composition should fall within the area A B C D of Figure 2 and annealed in the range of 1975 to 2025 F., i.e. at about 2000 F., transformed by cooling "to about -110 F. Thereafter such steels may be tempered in the range of 700 to 1100" F. and preferably at about 800 F. to produce the maximum properties. As indicated, such steels will have a Rockwell C value in excess of 45 or tensile strengths in excess of 220,000. Moreover, they are soft and ductile in the annealed condition.

If lower strengths and hardnesses are desired with attendant improvement in'ductile properties the following composition having lower carbon and higher nickel contents in conformity with the area ABCD of Figure l of the drawing may be used:

Percent Carbon .04 to .12 Manganese .75 to 1.20 Silicon .35 to .75 Nickel 4.7 to 7.0 Chromium 15. to 17.8 Vanadium .60 to 1.20

these embodiments are merely for the purpose of illustration and description and that various other f m may be devised within the scope of my invention, as defined in the appended claims.

I claim:

1. Stainless steel characterized by being transformable to a hard martensitic structure by sub-zero treatment from a soft austenitic structure in the annealed condition which can be tempered to improve the ductility thereof, said steel containing Percent Carbon .03 to .30 Manganese .50 to 2.00 Silicon .20 to 1.5 Nickel 3.0 to 7.5 Chromium 15.0 to 18.0 Vanadium .55 to 1.75

the ferrite formers being balanced to provide an M temperature between about0 F. and 50 F. with theremainder iron and other elements "in amounts which do not adversely affect the properties.

2. Stainless steel characterized by being transformable to a hard martensitic structure from a soft austenitic structure in the annealed condition which can be tempered to improve the ductility thereof, said steel containing Percent Carbon .15 to .26 Manganese .75 to 1.2 Silicon .35 to .75 Nickel 3.4 to 5i6 Chromium --16.0to 17.3 Vanadium .6 to -1.2

Percent Carbon .04 to .12 Manganese .75 to 1.2 Silicon .35 .to'.75 Nickel 4.7 to 7.0 Chromium .15 .0 to 17-8 Vanadium .6 to "1.2

the ferrite formers and the austenite formers being balanced to provide an M temperature between about 0 and 50 F. with the balance iron and other elements in amounts which do not adversely affect the properties.

4. Thermally hardened articles composed of'stainless steel containing Percent Carbon .03 to .30 Manganese .50 to 2.0 Silicon .20 to 1.5 Nickel 3.0 to 7.5 Chromium 15.0 to 18.0 Vanadium .55 to 1.75

wherein the austenite and ferrite formers are balanced -to provide an M temperaturebetween about 0 and 50 F. with the balance iron and other elements in amounts which do not adversely affect the properties, said steel having been annealed'at a temperature in the range of 1700" to 2100 F. and quenched to provide a soft austenitic readily formable structure and thereafter hardened by cooling it to below about -1 00 F. to transform it to a hard martensitic structure. g

5. Thermally hardened steel articles l'characterizedby a tensile strength inexcess .of 220,000 p.s.i. composed of stainless steel containing Per Carbon I .15 to .26 Manganese .75 to 1.20 Silicon "'.35to.75 Nickel I s I 3.40 to 5.6 Chromium 16.0 to 17.3 Vanadium ,.6.to 1.2

wherein the austenite formers and ferrite formers are balanced to provide an M temperature between about and -50 F. and the chromium, nickel and carbon are within the area A B C D of the drawing, with the balance iron and other elements in amounts which do not adversely afiect the properties, said steel having been annealed at a temperature in the range of 1975 to 2025 F. and quenched to provide a soft austenitic easily formable structure and thereafter hardened by cooling to below about -100 F. to transform it to a hard martensitic structure.

6. Thermally hardened steel articles composed of stainless steel containing wherein the austenite formers and ferrite formers are balanced to provide an M, temperature between about 0 and 50 F. and the chromium, nickel and carbon are within the area ABCD of the drawing with the balance iron and other elements in amounts which will not adversely afiect the properties, said steel having been annealed at a temperature in the range of 1775 to 1825 F. and quenched to provide a soft readily formable austenitic structure and thereafter hardened by cooling to below about -100 F. to transform it to a hard martensitic structure.

7. A method of producing hardened stainless steel comprising making stainless steel containing Percent Carbon .03 to .30 Manganese .50 to 2.0 Silicon .20 to 1.5 Nickel 3.0 to 7.5 Chromium 15.0 to 18.0 Vanadium .55 to 1.75

Percent Carbon .15 to .26 Manganese .75 to 1.2 Silicon .35 to .75 Nickel 3.4 to 5.6 Chromium 16.0 to 17.3 Vanadium .6 to 1.2

wherein the austenite formers and ferrite formers are balancedto provide an M temperature between about ,0 and '--50 F. and the chromium, nickel and carbon are within the area A B C D of the drawing, with thebalance iron and other elements which do not adversely affect-the properties, annealing said steel at a temperature in the range 1975 to 2025 F., quenching it to provide a soft readily formable austenitic structure and then cooling said annealed steel to below about -'-100 F. to transform it to a hard martensitic structure.

9. A method of producing hardened stainless steel comprising making stainless steel containing 'Percent .04 to .12 .75 to 1.20

wherein the austenite formers and ferrite formers are balanced to provide an M temperature between about 0 and 50 F. and the chromium, nickel and carbon are within the area ABCD of the drawing, with the balance iron and other elements which do not adversely afiect the properties, annealing said steel at a temperature in the range of 1775 to 1825 F. and quenching it to provide a soft readily formable austenitic structure, and then cooling said annealed steel to below about F. to transform it to a hard martensitic structure.

10. A method of producing articles of hardened stainless steel comprising making stainless steel containing Percent .03 to .30 .50 to 2.0

the ferrite formers and the austenite formers being balanced to provide an M temperature between about 0 and 50 F., with the balance iron and other elements in amounts which do not adversely affect the properties, annealing said steel at a temperature in the range of 1700 to 2100 F., quenching it to provide a soft austenitic readily formable structure, forming the desired articles therefrom and then cooling said annealed steel articles to below about 100 F. to transform the steel thereof to a hard martensitic structure.

11. A method of producing articles of hardened stainless steel comprising making stainless steel containing Percent .15 to .26 .75 to 1.2 .35 to .75 3.4 to 5.6 16.0 to 17.3 .6 to 1.2

*wherein the austenite formers and ferrite formers are balanced to provide an M temperature between about 0 and -50 F. and the chromium, nickel and carbon are within the area A B C D of the drawing, with the balance iron and other elements which do not adversely affect the properties, annealing said steel at a temperature in the range of 1975 to 2025 F., quenching it to provide a soft readily formable austenitic structure, forming the desired articles therefrom and then cooling said annealed steel articles to below about 100 F. to transform the steel thereof to a hard martensitic structure.

7 -l2r. ,-A method of producing articles of hardened stainless steel comprising making stainless steel containing I "Percent Carbon .04 to-.12 'Manganese 75 to 1.20 'Silicon .35 to .75

Nickel 4.7'to37.0 chromium 15;0 to $17.8 Vanadium -e 56101.2

wherein the austenite formers and ferrite formers are balanced to provide an M temperature betweenabout O and 50 F. and the chromium, nickel and carbon are the range of 177510182 5 and quenching-it to provide a soft "readily formabl'e austenitic structure, forming the desired articles therefrom, andthen cooling said annealed steel articles to below about l00 F. to transform the steel thereof to a hard martensitic stmcture.

iR efei-ences Cited in the file of this patent UNITED STATES PATENTS Binder July 31, 1951 "Lena July 16, 1957 

1. STAINLESS STEEL CHARACTERIZED BY BEING TRANSFORMABLE TO A HARD MARTENSITIC STRUCTURE BY SUB-ZERO TREATMENT FROM A SOFT AUSTENITIC STRUCTURE IN THE ANNEALED CONDITION WHICH CAN BE TEMPERED TO IMPROVE THE DUCTILITY THEREOF, SAID STEEL CONTAINING 